The potential benefits of inoculation with AM (arbuscular mycorrhizal)
fungi were investigated on Atlas Cypress (Cupressus atlantica G.), an
endemic Cupressacea in Morocco. The parameters under study were (i) the
growth of the plant, (ii) the functional diversity of soil microflora
and (iii) the rock phosphate (RP) solubilizing activity. C. atlantica
growth was measured after 12 months of culture in plastic bags arranged
in a randomised complete block design with 10 replicates per treatment.
Fungal inoculation consisted of either G. intraradices alone or a
mixture of native AM fungi. P amendment was supplied under the form of
Khouribga Rock Phosphate (KRP) powder. Microbial catabolic diversity was
assessed by measuring CO2 production of SIR (substrate induced
respiration) responses. Results showed that: (i) the fungal symbionts
were effective to improve the growth of C. atlantica, confirming the
requirement of mycorrhizal symbiosis for the successful establishment of
C. atlantica in a degraded soil; (ii) G. intraradices appeared to be the
most effective in promoting growth of C. atlantica, whereas indigenous
AM fungi were relatively ineffective. Native AM fungi inoculation
strongly modified functional abilities of the soil microflora, and in
the treatments with P amendment, growth stimulations of native AM fungi
inoculation were significantly higher than those of G. intraradices
inoculation for the shoot growth and leaf P content; (iii) C. atlantica
plants inoculated with native AM fungi could mobilize P from KRP more
efficiently than those mycorrhized with G. intraradices. A strong
interaction between KRP amendment and fungus inoculation was detected
for the leaf P content results. In conclusion, the use of a mixture of
native AM fungi combination may increase the chance of including one
very effective fungal isolate, but also, creates a more favourable
environment for the development of ecosystems processes.